SEMINAR LMGP - June 7, 2022 - Laetitia BARDET

Laetitia BARDET

PhD student,
Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000, Grenoble, France
Univ. Grenoble Alpes, CNRS, Grenoble INP, LGP2, F-38000, Grenoble, France

Abstract:

         
          Concerning transparent conductive materials, the great majority of scientific and industrial efforts have been devoted to transparent conductive oxides (TCO). Their relative high fabrication cost and their brittleness have a prompted search into alternative materials. The associated applications concern solar cells, efficient organic light emitting diodes, touch screens, smart windows or transparent heaters.^[1] In the last two decades, silver nanowire (AgNW) networks based transparent electrodes (TE) have been also the subject to many researches since they can exhibit several assets by combining good optical and electrical properties with high mechanical flexibility.

          After deposition, AgNW networks can still be resistive, mostly due to poor electrical contact at the nanowires junctions. Thermal annealing has been widely investigated as efficient post-deposition treatment to optimize the electrical resistance of AgNW networks.^[2][3][4] However, this treatment implies to control the temperature in order to prevent the degradation of AgNW networks and a low compatibility with heat-sensitive substrates, such as polymeric substrates for flexible devices. One of the objective of this work is to investigate capillary-force induced cold-welding using spray-coater equipment at low-temperature (100 °C) and compare the latter with thermal annealing. We demonstrate that cold-welding treatment not only enables to decrease the electrical resistance with similar efficiency as a thermal treatment but it decreases also the surface roughness of the network, which is a clear asset for integration with thin active layers such as second and third generation solar cells.

          One other drawback of AgNW networks that needs to tackle for efficient integration within devices are thermal, electrical and chemical instabilities. Several oxide coatings including zinc oxide (ZnO)^[5] deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) have been previously investigated to protect AgNW networks. This deposition process works in open-air at low temperature and is compatible with large-scale production; it is then expected to open a large field of further investigations and applications. In this work we consider the effects of conformal tin oxide (SnO₂) coatings deposited for the first time on AgNW networks by AP-SALD at 200 °C. The resulting Joule heating can lead to the degradation of AgNW networks when subjected to high applied electrical stress. By coupling both experimental data and a simple model with no fitting parameters, we predict the areal power densities range and the associated Joule heating that bare and SnO₂-coated AgNW networks can stand before experiencing irreversible modifications (i.e. morphological degradation). Such approach helps to deduce any irreversible behavior by minimizing the number of experimental observations. In addition, we also study the stability of SnO₂/AgNW nanocomposites when subjected to thermal stress up to 400 °C by measuring in situ both electrical resistance and X-Ray Diffraction. We also study the stability of these nanocomposites under humidity stress at 80 % HR and 70 °C for two weeks. In summary, we show that even thin layers of SnO₂ protect efficiently AgNW from morphological change under electrical, thermal stress and humidity stress. We report the development of stable TE with SnO₂/AgNW nanocomposites and open the door for efficient integration in optoelectronic devices, energy harvesting or energy storage devices.

Associated references

[1] V. H. Nguyen, D. T. Papanastasiou, J. Resende, L. Bardet, T. Sannicolo, C. Jiménez, D. Muñoz‐Rojas, N. D. Nguyen, D. Bellet, Small 2022, 2106006.
[2] D. P. Langley, M. Lagrange, G. Giusti, C. Jiménez, Y. Bréchet, N. D. Nguyen, D. Bellet, Nanoscale 2014, 6, 13535.
[3] L. Bardet, D. T. Papanastasiou, C. Crivello, M. Akbari, J. Resende, A. Sekkat, C. Sanchez-Velasquez, L. Rapenne, C. Jiménez, D. Muñoz-Rojas, A. Denneulin, D. Bellet, Nanomaterials 2021, 11, 2785.
[4] M. Lagrange, D. P. Langley, G. Giusti, C. Jiménez, Y. Bréchet, D. Bellet, Nanoscale 2015, 7, 17410.
[5] A. Khan, V. H. Nguyen, D. Muñoz-Rojas, S. Aghazadehchors, C. Jiménez, N. D. Nguyen, D. Bellet, ACS Appl. Mater. Interfaces 2018, 10, 19208.